Material removal rate measures how much metal actually leaves the workpiece per minute: in³/min in imperial, cm³/min in metric. Each operation has its form — MRR = feed × depth of cut × width of cut for milling, π/4 × D² × feed for drilling (the full hole cross-section advancing at the feed rate), and the handbook’s 12·V·f·d form for turning. The face-milling example runs the chain end to end: a 3.1 in/min feed with a 0.5 in axial depth and 0.25 in radial width removes 0.38 in³/min.
MRR is the number that ties a proposed cut to what the machine can deliver. Removing a cubic inch of steel per minute takes very roughly one spindle horsepower — the Machinery’s Handbook tabulates specific power by material — so if the removal rate times the material’s unit power exceeds what the spindle can supply, the cut stalls or stalls the feed, and the fix is reducing depth, width, or feed until the demand fits the machine.